In gas turbine engines a turbine operated by combustion product gases drives a compressor which furnishes air to a burner. Gas turbine engines operate at relatively high temperatures, and the capacity of such an engine is limited to a large extent by the ability of the turbine blades to withstand the thermal stresses that develop at such relatively high operating temperatures. The ability of the turbine blades to withstand such thermal stresses is directly related to the materials from which the blades are made, and the material's strength at high operating temperatures.
To enable higher operating temperatures and increased engine efficiency without risk of blade failure, hollow, convectively cooled turbine blades are frequently utilized. Such blades generally have intricate interior passageways which provide torturous, multiple pass flow paths to assure efficient cooling that are designed with the intent that all portions of the blades may be maintained at relatively uniform temperature. However, as cooling air flows through the relatively long interior passageways, a significant portion of the cooling air escapes through cooling holes in the side walls of the blade to provide film cooling.
This reduces the pressure, velocity, and mass flow rate of the cooling air as it flows through the interior passageways which reduces the rate at which heat from the turbine blade is transferred to the cooling air. Localized overheating of the side walls may occur in the side walls immediately adjacent the areas where the cooling airflow pressure, velocity, and mass flow rate are reduced. As a result of such overheating, the turbine blade may be weakened or damaged, thereby shortening the useful life of the turbine blade.
What is needed is a turbine blade that maintains cooling air pressure, velocity, and mass flow rate at such levels as to avoid localized overheating of the turbine blade.